A new basic peptide antibiotic of the tuberactinomycin group has been isolated from the culture broth of an artificial mutant derived from the streptomyces producing tuberactinomycin1). The antibiotic, named tuberactinomycin-N, showed somewhat stronger antituberculous activity and lower ototoxicity than the tuberactinomycin obtained from the parent strain. The isolation, characterization and properties of tuberactinomycin-N are described in this paper.